The International Monetary Fund (IMF) says Afghanistan is experiencing a "large influx" of returning refugees that is severely testing the country's ability to absorb so many displaced people.
In a report issued this week, the IMF said more than 700,000 refugees returned to Afghanistan last year, mainly from Pakistan, but also from Iran, Europe, and elsewhere.
"This is seriously aggravating the government's capacity to absorb refugees in an already difficult environment of high unemployment and internally displaced people after decades of conflict," it said.
The organization urged the country to strengthen internal coordination and planning and said the international community needs to play a role in providing financing and humanitarian support to avert a crisis.
The IMF said that many of those coming from Pakistan are not coming "voluntarily."
It said analysts estimate that up to 2.5 million more will return over the next 18 months, representing almost 10 percent of the Afghan population.
Decades of war and instability have driven millions of Afghans from their homes and out of the country.
Millions of refugees returned to Afghanistan after the U.S.-led invasion of 2001 drove the Taliban from power, but security has deteriorated since 2014, when most NATO combat forces had withdrawn from the country.
The security situation now remains difficult in many areas of the country, with militant groups like the so-called Islamic State (IS) battling Afghan government forces and remaining U.S.-led forces.
"Many of the Afghans who lived abroad for decades are returning to a country facing conflict, insecurity, and widespread poverty," the IMF said.
"Given the difficult economic climate, prospects for returnees are generally poor," it added. 'While there are also wealthier returnees, a typical returning refugee has a high risk of falling into poverty.